The present invention relates to a rolling element for use in a rolling member and a bearing which constitute a toroidal continuously variable transmission (CVT) for automobiles, a bearing constituting an engine driving auxiliary machinery such as a fuel pump, an alternator and an air compressor, or a bearing for an air compressor, a gear and a bearing for a transmission, and relates to a process for producing the rolling element. More specifically, this invention relates to a rolling element which is improved in rolling-fatigue strength and significantly prevents short-life peeling or flaking due to hydrogen-induced embrittlement that will be caused when hydrogen generated by decomposition of a lubricating oil during rolling of the rolling element penetrates into a metal material of the rolling element, and a process for producing the rolling element.
U.S. Pat. No. 5,510,974, corresponding to Japanese Patent Application First Publication No. 2-190615, describes a grease-sealed bearing aiming at suppressing hydrogen infiltration into races of the bearing, namely, the short-life peeling or flaking due to hydrogen-induced embrittlement as described above. The races have triiron tetroxide layers on the rolling surfaces which are formed by blackening treatment to thereby restrain the occurrence of flaking on the bearing surfaces and improve lives of the bearing.
Japanese Patent Application First Publication No. 6-313434 describes a corrosion resistant rolling bearing in which a nickel plating layer is formed on a surface of at least one of an inner race, an outer race, rolling members and a retainer for the rolling members. This technology contemplates to improve corrosion resistance under the severe corrosive environment such as salt water spraying and enhance the plating ability.